The long term goal of this proposal is an understandig of the role of prolactin in ovarian function. Previous work from this laboratory has demonstrated specific prolactin receptors on porcine ovarian cells, and dramatic changes in prolactin binding during the reproductive cycle and pregnancy. The experiments here are designed to answer two questions raised by these studies: (a) What hormonal or developmental influences control or modulate prolactin binding in the ovary? Preliminary data in this area has indicated that suspension and monolayer cultures of porcine granulosa cells will be suitable for study of receptor development in vitro. To complement this in vitro work, we will investigate receptor development during hormone-induced ovarian differentiation in immature pigs. This combined approach will allow precise definition of factors which influence binding. (b) How do the observed changes in binding relate to prolactin responsiveness of the ovary? An answer to this question will require definition of suitable parameters to allow an understanding of prolactin action in terms of physiological or biochemical ovarian responses. In this regard, preliminary evidence suggests that progesterone secretion and prostaglandin F2 alpha secretion, both suppressed by prolactin in vitro, will serve as suitable markers for this purpose. We will relate these changes to receptor activity and search for other potential actions of prolactin on the ovary in vivo and in vitro. Since reproductive processes in the pig are similar to those of human, we anticipate that this research will provide answers to important clinical questions regarding prolactin-related menstrual disturbances in women.